This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Smallpox is a life threatening disease caused by exposure to variola virus, a highly contagious pathogen that is considered a biological threat agent. In the event of an accidental or deliberate aerosol exposure of variola, there are currently no recommended drugs for postexposure prophylaxis and/or treatment for smallpox. Cidofovir is an antiviral drug that can be used to treat infection in the event of a biological attack. An inhaled cidofovir dry-powder formulation is being developed for post-exposure prophylaxis and treatment of aerosol exposure to variola. Inhaled cidofovir has been shown in multiple mouse studies to be highly efficacious against various pox models, producing long-term activity and retention in the lung tissue compared to injectable administration. Intravenous administration of cidofovir, although efficacious, results in lower lung levels, severe kidney toxicity, and requires a health-care worker to implement treatment. Inhalable cidofovir, alternatively, results in high drug levels in the lung, bypasses the kidneys, and is self-administered. Initially, we used a pharmaceutical-grade powder version of cidofovir (NanoFOVIR;Nf) to treat rabbits exposed to aerosolized rabbitpox virus (RPXV) to further evaluate the effectiveness of direct drug delivery to the lung. Na[unreadable]ve rabbits were infected by aerosol with H10-50 LD50 of RPXV. Three subsets received aerosolized Nf at either 0.5, 1.0 or 1.75 mg/kg daily for 3 days postinfection (PI) at t=0h. Another subset received either IV-cidofovir (10 mg/kg daily, 3 days PI), or were untreated (CRL). Results showed Nf groups showed an antiviral-dose associated survival of 50% (0.5), 80% (1.0) and 100% (1.75). All animals in the IV-cidofovir group survived;all CRL animals died day 5-6 PI. Acute clinical signs of RPX disease, including anorexia, hyperthermia, rhinorrhea, dyspnea, tachycardia and poxviral rash, developed in the CRL +3d PI until death. Nf (0.5, 1.0) and the IV-cidofovir groups experienced milder clinical signs vs CRLs. The Nf (1.75) group showed minimal clinical response to RPX and a dose-related blunting of lung lesions vs CRL or IV-Cr groups. Nf protected rabbits from RPX at H10% of the equivalent IV-Cr dose. A dose-related effect was observed in clinical development of RPX disease in Nf groups. Significant reduction of RPX-induced pathological changes was observed in Nf (1.75) and IV-cidofovir groups. Results suggest that inhalable Nf may be a viable antiviral for emergency PEP and should be evaluated in other models of poxviral disease (e.g., MPX in nonhuman primates). Results of these studies will establish the relative safety and preclinical efficacy of reformulated cidofovir as a viable antiviral therapeutic against smallpox.